1. Field of the Invention
The present invention relates to a flat type vibration motor, and more particularly to a flat type vibration motor in which a weight of high specific gravity is provided on an upper substrate having a winding coil to ensure stable vibration characteristic and facilitate a slim size of the motor.
2. Description of the Prior Art
In general, one of functions essentially required for a communication system is a termination(incoming call) function. For such a termination function, vocalization such as melody and bell or vibration for vibrating the communication system is mostly used.
In other words, if a user in advance selects a function required for termination, the selected function is working during termination to allow the user to sense the termination.
In such a termination function, particularly, the vibration function is mainly used so as to avoid noise pollution in a place crowded with people.
The vocalization function such as melody or bell is intended to sense termination by externally transferring various kinds of melodies or bells, which are in advance input inside the system, through a small sized speaker. The vibration function is intended to vibrate the system by driving a small sized vibration motor to transfer the vibration force to a case of the system.
Meanwhile, the previously used vibration function is working by a vibration motor separately mounted in the system. The most representative example of the vibration motor is a flat type vibration motor called a pan cake or coin type having a relatively large diameter as shown in FIG. 1.
The flat type vibration motor includes a fixed member, i.e., a stator, and a rotating member, a rotor r. The stator includes a magnet 3 and a case. The stator is electrically connected with the rotor r by a brush 7b. 
In other words, a lower substrate 2 printed with a circuit on its surface is attached to an upper surface of a lower case 1 which is a round shaped flat panel. A doughnut shaped magnet 3 is attached to an upper surface of the lower substrate 2.
At this time, since the lower substrate 2 is attached to a part of the upper surface of the lower case 1, the magnet 3 is widely attached to the lower case 1 and the lower substrate 2.
The upper surface of the lower case 1 is covered by a cap shaped upper case 4 which is open downwardly. The lower case 1 and the upper case 4 are firmly connected with each other at their central portions by a shaft 5.
Meanwhile, a hard board has been used as the lower substrate 2 attached to the lower case 1. Recently, a flexible board is mainly used as the lower substrate 2.
In the aforementioned constitution, the stator is provided, and the rotor r is provided around the shaft 5 in the stator.
The rotor r includes an upper substrate 6 and a commutator 7a. The upper substrate 6 is eccentrically supported in the shaft 5 by cutting a round shaped flat panel at a predetermined angle. The commutator 7a includes a plurality of segments on the circumference at the bottom of a rotation central portion supported in the shaft 5 of the upper substrate 6. A winding coil 8 is attached to the upper surface of the rotor, and an insulator 9 of a general resin is integrally formed by injection molding on the upper surface of the upper substrate 6 other than the attachment surface of the winding coil 8.
In the motor which includes the stator and the rotor r, externally input power source is induced through the lower substrate 2, and the power source induced to the lower substrate 2 is supplied to the commutator 7a through the brush 7b. 
The brush 7b includes a pair of power input and output brushes. These brushes are separated from each other at a constant angle. The bottom of the respective brush is fixedly connected to a circuit of the lower substrate 2 and its top portion is slidably contacted with the segments of the commutator 7a. 
Accordingly, the current induced through the lower substrate 2 is transferred to the commutator 7a through the brush 7b at one side and to the winding coil 8 through the upper substrate 6. The current flows from the winding coil 8 to the upper substrate 6, the commutator 7, and the brush 7b at the other side. Thus, the winding coil 8 is always electrically connected. At this time, electromagnetic force is generated by mutual action between the winding coil 8 and the magnet 3 to obtain driving force.
At this time, since the rotor r is eccentrically supported in the shaft 5, the rotor r is eccentrically driven. Such eccentric driving force is externally transferred through the shaft 5 so as to vibrate the system.
Therefore, the performance of the vibration motor depends on the vibration amount. Since the vibration amount depends on the eccentric amount of the rotor r, it is difficult to obtain the required eccentric amount by a structure in which the upper substrate 6 is cut at a predetermined angle with respect to a round shape and the winding coil 8 is eccentrically arranged on the upper substrate 6 with respect to the rotation center.
In this respect, in the rotor r of the currently used vibration motor, the winding coil 8 is arranged on the upper substrate 6 and the insulator 9 is filled around the winding coil 8. At this time, a resin material containing metal of high specific gravity such as tungsten is used as the insulator 9 to provide the required eccentric amount. Thus, the sufficient vibration amount can be obtained.
In the aforementioned rotor r, as shown in FIG. 2, the winding coil 8 is arranged at both sides of the upper substrate 6, and the winding coil 8 is integrally coupled to the upper substrate 6 by insert injection through the insulator 9 so that the eccentric amount in the rotor r can be enhanced.
However, since the insulator 9 which couples the upper substrate 6 with the winding coil 8 by insert injection contains a metal component having high specific gravity such as tungsten, the fluidity of the insulator 9 is not good due to the tungsten component which is not likely to be melted.
Accordingly, high pressure is required during insert injection by the insulator 9. The upper substrate 6 and the winding coil 8 are deformed or short of the circuit is caused due to pressure applied by the insert injection. For this reason, the poor product is caused. Particularly, the productivity is deteriorated due to difficulty of the injection operation.
Furthermore, the insulator 9 of a high specific gravity material is substantially occupied in the rotor r at a small eccentric weight ratio. Moreover, as shown in FIG. 2, if the insulator 9 is partially formed toward the other side corresponding to one side at the center supported in the shaft 5, the insulator 9 formed at the other side decreases the eccentric amount of the rotor r, thereby deteriorating the eccentric driving force by the rotor r.
Finally, since the insulator 9 of a high specific gravity material is very expensive in view of its function performed in the rotor r, it is not economical.
It is, therefore, an object of the present invention to provide a flat type vibration motor in which a weight is provided on a round shaped upper substrate having a winding coil to prevent the eccentric amount from being reduced due to a slim thickness of the rotor, thereby facilitating a slim size of the motor.
Another object of the present invention is to provide a flat type vibration motor, in which an upper substrate is formed in a round shape to a separate cutting process is omitted, thereby reducing the production process time.
Other object of the present invention is to provide a flat type vibration motor in which the eccentric amount by the weight is maximized to improve the vibration performance of the slim sized motor.
To achieve the above object, there is provided a flat type vibration motor according to the present invention including: a lower case; an upper case which covers an upper portion of the lower case; a shaft which connects the center of the lower case with the center of the upper case and supports them; a lower substrate attached to one portion on an upper side of the lower case; a magnet attached to the lower substrate and the upper side of the lower case; a round shaped thin upper substrate rotatably supported in the shaft; a commutator provided with a plurality of segments on the circumference of the center of the shaft at the bottom of the upper substrate; a pair of brushes of which one end is fixed to the lower substrate and other end is in contact with the commutator to be electrically connected with the commutator; a pair of winding coils arranged separated from each other at a constant angle toward one side of the upper substrate; a weight of high specific gravity arranged toward the other end of the upper substrate corresponding to the winding coil; and an insulator of resin filled between the winding coils and the weight, for firmly fixing the winding coils and the weight to the upper substrate.
In another aspect, there is provided a flat type vibration motor according to the present invention including: a lower case; an upper case which covers an upper portion of the lower case; a shaft which connects the center of the lower case with the center of the upper case and supports them; a lower substrate attached to an upper side of the lower case; a magnet attached to the lower substrate and the upper side of the lower case; an upper substrate rotatably supported in the shaft and unevenly formed to be eccentrically supported in the shaft by cutting a round shaped thin plate at a predetermined angle; a commutator provided with a plurality of segments on the circumference of the center of the shaft at the bottom of the upper substrate; a pair of brushes of which one end is fixed to the lower substrate and other end is in contact with the commutator to be electrically connected with the commutator; a pair of winding coils arranged separated from each other at a constant angle toward one side of the upper substrate; a weight of high specific gravity arranged between the winding coils; and an insulator of resin filled between the winding coils and the weight, for firmly fixing the winding coils and the weight to the upper substrate.